Determination of the physical characteristics of cutting piles, using existing survey data and drilling information

Abstract

From the Conclusions: “From data received during this and earlier studies, equations have been derived that describe the relationship between the in situ volume of cuttings piles and predictors such as the volume of discharged cuttings, water depth, caisson depth and number of wells. From these equations, and mapping data received from operators, an estimate has been made of the range of physical characteristics of cuttings piles on the seabed that lie beneath multi-well installations in the central and northern North Sea.

Data were received, during this and earlier studies, describing the internal composition of cuttings piles, but a small number of coring studies has been conducted. Meaned data from 15 developments indicated that there was no obvious depth distribution pattern of THC or PAH concentrations.

Distribution patterns of other parameters, which included metals, bacterial numbers, Eh and pH, were equally unclear. SRB numbers were positively correlated with concentrations of total hydrocarbons, negatively with arsenic, but not at all with concentrations of PAH. Other anaerobic bacterial numbers were negatively correlated with concentrations of PAH and arsenic.

Variabilities in the distribution of contaminants through the piles were ascribed to operational disruption of the cuttings piles on the seabed, perhaps further compounded by physical disturbance during sampling.

It is concluded that in order to determine accurately the physical and chemical composition of cuttings piles, that a suitable sampling programme would be required followed by laboratory analysis of a variety of parameters. Such survey programmes should be site specific and be tailored to the particular pile dimensions at a location.”